This invention relates to a gas pressure relief device. More particularly, this invention relates to a liquid column safety relief device for use on a process or pipeline.
There are several gas pressure relief safety devices available to industry. Such devices are used to relieve a pressure surge to avoid damage to personnel or equipment.
Mechanical devices such as valves have the disadvantage of frequent maintenance to prevent leakage, to maintain set relieving pressure, and to assure operability. The valves are generally not available in sizes over a 12 inch inlet diameter. The spring and pallet loaded type valves leak at pressures closer than 10% of the set relieving pressure. The pilot operated type valves have elastomer parts that limit their application. Chattering, that is, rapid opening and closing of the valve during discharge, can destroy valve seats or entire valves.
Rupture disks avoid the maintenance encountered with use of a valve, but the disks must be replaced after each relief. The rupture disks also do not close to retain the process contents after relieving and are subject to corrosion and fatigue which can cause leaking and accidental relieving below the set relieving pressure.
Another known gas pressure relief safety device is the liquid filled U-leg. The U-leg safety device is essentially a downward loop of pipe partially filled with liquid. This device solves the cost, maintenance, and leakage faults of the valves and rupture disks, but, like the rupture disk, it does not close to retain the process contents after relieving. When the U-leg discharges, the liquid is blown from the U-leg and entrained in the discharging gasses. Attempts to refill the leg without stopping the gas flow, result in the liquid being blown through as fast as it is introduced. Therefore, the process must be interrupted in order to refill the liquid leg.
It is desired to solve the problems associated with the above prior art devices by providing a novel gas pressure relief device which will seal reliably from full vacuum to the set relieving pressure, will relieve a pressure surge without interrupting the process on which it is installed, and will relieve dependably at the precise set relieving pressure.
More particularly, it is desired to provide a liquid-column safety device which has the following important advantages over safety valves and rupture disks:
1. The liquid-column can be built for relief of very low pressures, for example about 0.05 psig. PA0 2. The liquid-column can be built in very large sizes not available in other safety relief devices. PA0 3. The liquid-column does not leak or simmer when operated at pressures near the relief pressure. PA0 4. The liquid-column's relief pressure is accurate and does not require frequent calibration and maintenance. PA0 5. The liquid-column's resealing pressure is precise, predictable, and the same as it's relieving pressure. PA0 6. The liquid-column does not wear out or destroy itself by bursting (rupture disk) or chattering (safety valve) while relieving. PA0 7. The relieving pressure of the liquid-column can be changed without interrupting the process, e.g., the liquid-column can be set to relieve at different pressures by varying the amount of liquid in the column without interrupting the process. PA0 8. The liquid-column can handle hot discharged which will be cooled and diluted by the liquid-column's seal liquid which, in turn, will reduce the hot discharges' volume and flammability. PA0 9. The liquid-column does not contain any soft seats which can be damaged by hot discharges. PA0 10. The noise level caused by relieving gas through the liquid-column is much lower. PA0 11. The liquid-column does not require replacement after a relief. PA0 12. The liquid-column can operate safely much closer to the relieving pressure. PA0 13. The liquid-column's relieving pressure is precise. PA0 14. The liquid-column's relieving pressure is not affected by corrosion or fatigue.